Draw a Fischer projection for each compound. Remember that the cross represents an asymmetric carbon atom, and the carbon chain should be along the vertical, with the IUPAC numbering from top to bottom.
(c) (S)-1,2-dibromobutane
(d) (R)-butan-2-ol

Verified step by step guidance

1. Understand the Fischer projection: A Fischer projection is a two-dimensional representation of a molecule where the vertical lines represent bonds going away from the viewer (into the plane), and the horizontal lines represent bonds coming toward the viewer (out of the plane). The carbon chain is placed vertically, with the highest-priority functional group at the top.
2. For (S)-1,2-dibromobutane: Start by drawing the carbon chain vertically with four carbons. Place the bromine atoms on the first and second carbons. Assign priorities to the substituents on the second carbon (asymmetric center) based on the Cahn-Ingold-Prelog (CIP) rules. Ensure the configuration is (S) by arranging the substituents such that the lowest-priority group is pointing away (on the vertical line).
3. For (S)-1,2-dibromobutane: After assigning priorities, confirm the (S) configuration by tracing the path from the highest to the lowest priority (1 → 2 → 3) in a counterclockwise direction. Adjust the substituents on the Fischer projection to reflect this configuration.
4. For (R)-butan-2-ol: Start by drawing the carbon chain vertically with four carbons. Place the hydroxyl (-OH) group on the second carbon. Assign priorities to the substituents on the second carbon (asymmetric center) using the CIP rules. Ensure the configuration is (R) by arranging the substituents such that the lowest-priority group is pointing away (on the vertical line).
5. For (R)-butan-2-ol: After assigning priorities, confirm the (R) configuration by tracing the path from the highest to the lowest priority (1 → 2 → 3) in a clockwise direction. Adjust the substituents on the Fischer projection to reflect this configuration.

Key Concepts

Fischer Projections

Fischer projections are a two-dimensional representation of three-dimensional organic molecules, particularly useful for depicting stereochemistry. In these diagrams, vertical lines represent bonds that project behind the plane of the page, while horizontal lines represent bonds that project out towards the viewer. This format is especially helpful for visualizing the configuration of chiral centers in molecules.

Stereochemistry

Stereochemistry is the study of the spatial arrangement of atoms in molecules and how this affects their chemical behavior. It is crucial for understanding isomers, particularly enantiomers, which are non-superimposable mirror images of each other. The (R) and (S) designations indicate the specific three-dimensional arrangement of substituents around a chiral carbon, which is essential for accurately drawing Fischer projections.

Chiral Centers

A chiral center, often a carbon atom, is bonded to four different substituents, leading to non-superimposable mirror images. The presence of chiral centers in a molecule results in optical isomerism, where two enantiomers can exhibit different optical activities. Identifying chiral centers is vital for correctly representing the stereochemistry of compounds like (S)-1,2-dibromobutane and (R)-butan-2-ol in Fischer projections.